Cathode coupled magnetron system



June 12, 1962 D. A. WILBUR' ETAL 3,039,019

CATHODE COUPLBDMAGNETRON SYSTEM Filed Aug. 19. 1959 In ventor-s:

Thai t'to r'ney Dona /d A. Wi/bur; Phi/1P H. Peter-s Jr;

United States Patent 3,039,019 CATHODE COUPLED MAGNETRON SYSTEM Donald Wilbur, Scotia, and Philip H. Peters, In,

Greenwich, N.Y., assignors to General Electric Company, a corporation of New York Filed Aug. 19, 1959, Ser. No. 834,790

Claims. (Cl. 315-3953) The present invention relates to an improved magnetron system having the power output circuit coupled :hrough the cathode and more particularly to such a. :ystem which is particularly suited for voltage tuning.

In the use of magnetrons, particularly of the interdigital :ype, as oscillators, it is common practice to couple output power to a waveguide, the opposite Walls of which are connected to the spaced and mutually insulated anode terminals to which the interdigital anode sections are connected. In such an arrangement it is difiicult to load the anode circuit uniformly around the circumference of the magnetron with the output circuit. This is due partially to the difficulty of providing uniformly good contact throughout the circumference of the anode terminals. This is particularly important in magnetron systems intended for voltage tuning, that is, systems in which the oscillating frequency is to be adjusted by adjusting the anode-cathode voltage. As described in detail and claimed in US. Patent No. 2,774,039, dated December 11, 1956, such voltage tuning may be accomplished if the number of electrons in the interaction space is suitably limited and if the anode circuit is heavily loaded. The heavy and uniform loading desired for this type of operation may be more readily attained by coupling the output power through the cathode circuit in accordance with the present invention. The lack of uniformity of loading with the conventional anode coupled output circuit tends to result in substantial power generated in other than the desired mode. Also, as the frequency of operation increases, the difficulty of obtaining the desired loading in the more conventional anode coupled output becomes increasingly difficult.

It is an important object of the present invention to provide an improved magnetron system having a cathode coupled output circuit.

It is another object of this invention to provide an im provedmagnetron system which is particularly suited for voltage tuning. It is a further object of this invention to provide an improved magnetron system in which the cathode structure provides a portion of a concentric lineto-wave guide output transition circuit.

In interdigital magnetron circuits, for example, the anode structure is rather well coupled to the cathode. Both sets of vanes are, however, equally coupled and significant transmission of power from the cathode circuit does not result. In accordance with our invention the coupling between the two sets of vanes is made unequal and specifically this is accomplished by providing a very substantial capacitive coupling between one set of theanode sections and the cathode as compared 'with that existing between the other set of anode sections and the cathode. The end of the cathode structure remote from that which is closely coupled to the anode is made a: portion of a transition circuit from a concentric line to a waveguide so that the termination of the central cathode structure and the anode may form the opposite side walls of an output waveguide for coupling power from the cathode circuit t the utilization circuit. In the preferred embodiment illustrated the magnetron device is particularly suited for voltage tuning and includes the feature of electron injection into the interaction space in accordance with the energization of a control electrode. The control electrode in turn is shaped to provide a sub- 3,039,019 Patented June 12, 1962 stantial part of the high capacity coupling circuit between one set of the anode sections and the cathode circuit.

Further objects and advantages of our invention will become apparent as the following description proceeds reference being had to the accompanying drawing and its scope will be defined in the appended claims. In the drawing FIGURE 1 is an elevational view in section of a magnetron device and output circuit embodying our invention;

FIGURE 2 is a sectional view taken along the line 2-2 of FIGURE 1;

FIGURE 3 is an enlarged elevational view in section of a portion of the cathode structure shown in FIGURE 1; and

FIGURE 4 is a schematic illustration of a lumped circuit equivalent of the circuit embodied in the structure of FIGURES 1-3, inclusive.

In the embodiment of the invention illustrated in FIG- URE 1 an interdigital type of magnetron device designated generally by the numeral 10 is mechanically secured in position in a waveguide 11 of rectangular crosssection by means of an annular clamping ring 12 having threaded engagement with the waveguide and a lip 13 engaging a corresponding lip 14 on an annular anode terminal 15 of the magnetron device. The device 10 is made up of a generally cylindrical hermetically sealed envelope including in addition to the anode terminal 15 an annular control electrode terminal 16 separated therefrom by an annular ceramic spacer 17. The ends of the envelope are closed by ceramic disks 18 and 19 which are somewhat cup-shaped and the edges of which are sealed respectively to the control electrode terminal 16 and the anode terminal 15.

The anode circuit is in the form of a radial cavity resonator having annular end walls provide-d by upper and lower plates 20 and 21 supported in axially spaced relation from the anode terminal 15 by means of a generally annular member 22 of T-shaped cross section. In a particular embodiment constructed in accordance with our invention the annular end plates 20 and 21 were of copper, the anode terminal 15 of titanium and the T shaped annular ring 22 of molybdenum. Interaction with the electrons is accomplished by an array of anode sections, alternate ones of which are supported from the plates 20 and 21, respectively. As illustrated the anode sections 23 are supported from the upper plate 20 and the alternate anode sections 24 are supported from the lower plate 21.

A control electrode 35 is supported from the control electrode terminal 16 and as illustrated is formed integrally therewith. The control electrode is a'relati-vely massive annular ring having an extended surface in close proximity to the upper surface of the anode cavity and having the inner edge thereof concentric with the inner surface of the array of anode sections 23 and 24. The surface 36 defining the central opening in the control electrode is generally frustoconical in shape with the smaller end of the opening adjacent the anode structure. The control electrode also provides a support for one end of the cathode structure. As illustrated a generally annular cathode terminal ring 37 is seated in an annular insulating ring 38 which is, in turn, received in a suitably shaped annular recess 38' formed in the upper surface of the control electrode 35. This cathode terminal ring 37 may to advantage be formed of titanium, the same material as the control electrode 35. The control electrode 35, the insulator 38 and the terminal ring 37 may be bonded together to form a unitary supporting structure. Asmall molybdenum insert 39 may be provided as the direct The other end of the cathode sleeve is connected by means of a nickel foil collar 42 to the upper end of a non-emitting cathode post 43. This post is supported at its lower end from a frustocon-ically shaped member 44 of larger diameter than the non-emitting post and which terminates in a circular flange 45 gaging the inner surface of the lower end wall 19 and providing for the capacitive coupling of the cathode to the lower wall 46 of the wave guide. This circular flange 45 may also to advantage be bonded to the end wall provided by ceramic disk 19 of the envelope. As illustrated the cathode sleeve 40 is substantially cup-shaped having an end wall which provides a heat shield between the spiral heater 47 and the nonemitting post 43 to limit the heat transfer from the heater element to the support. Terminals for the heater and for the cathode are provided by titanium disks 48 and 49 bonded to the exterior of the upper end cap 18 of the envelope. As illustrated, one lead 50 of the heater 47 is connected with terminal 48 and the other lead heater is connected to the cathode terminal ring 37 which is, in turn, connected to the cathode terminal 48 by means of a pin 51. Thesystem illustrated in FIGURE 1 may be energized for operation as an oscillator as follows: A suitable voltage for energizing the heater element 47 is applied to the terminals 48 and 49. The anodecathode voltage for providing a radial electric field in the interaction space between the non-emitting cathode 43 and the anode sections 23 and 24 is applied between cathode terminal 50 and the anode terminal 15. For voltage tuning applications this voltage is, of course, made adjustable. The control electrode 35 is connected to a control voltage to determine the number of electrons emitted from the coated electrode sleeve 40 that are injected into the interelectrode space. A suitable axially directed magnetic field is produced either by permanent or electro magnets. (not shown). In our prior Patent 2,810,096,

dated October 15, 1957, a magnetron system providing" for the injection of electrons in the interaction space and suitable for voltage tuning, is described and claimed. In the system there described the output waveguide is coupled to two spaced anode terminals which are insulated with respect to one another and connected to the array of anode sections. In accordance with the present invent-ion the anode sections form the inner wall of a radial cavity, the dimensions of which determine the center frequency of operation of the system and the high frequency power generated by the oscillator is supplied to the output waveguide 11 through the cathode circuit. A better understanding of this aspect of the present invention may be had by considering the schematic diagram of FIGURE 4 in conjunction with the structure of FIGURES 1 and 2 already described. Referring now to the circuit of FIG- URE 4 of the drawing, the anode cavity is represented by the parallel tuned circuit L and C and the capacitances C, and C represent the coaxial capacitances between the two sets of anode sections and the cathode. While this coupling is substantial, the high frequency voltages are of opposite polarity and if the anode sections are reasonably short axially, the effects of this coupling tend to cancel out. The capacity provided in accordance with the present invention makes possible the effective transmission of power from the anode through the cathode circuit is the relatively large coupling capacity between one set of anode sections and the cathode and is represented at C In the illustrated embodiment of the invention, the capacity C is provided by the extended area of the control electrode 35 in close proximity to the upper wall of the anode resonat and the anode sections connected thereto and also by the coupling capacity between the control member and the cathode provided by the extended and closely spaced surfaces separated by the insulator 38. The shunting inductance L is the inductive impedance between the upper group of anode sections and the cathode ring 37. The-inductance L is the distributed inductance of the non-emitting cathode. L represents the inductance of of electron injection the conical matching portion of the cathode which extends into the area enclosed by the waveguide 11 and C is the series capacity introduced by the thin ceramic wall between the flange 45 of the cathode structure and the bottom wall of the waveguide. C is the shunt capacitance introduced by the cylindrical portion of the ceramic member 19 and R is the useful resistive load associated with the waveguide. It is contemplated that the region will appear inductive over most of the tuning range and that the capacitance C; can be made of proper size to be series resonant with this inductive reactance so as to transfer maximum power to the waveguide over the widest possible bandwidth. The capacitance C is resonated with the inductance of an iris (schematically represented in FIGURE 4 at L suitably extending across the waveguide 11 a short distance from the tube in the direction of energy transmission. The geometry of the coupling system may be readily designed so that the bandwidth thereof is at least as great as that of the loaded anode cavity.

From the foregoing detailed description it is apparent that our invention provides a simple magnetron structure which is effective to provide an unbalance in the coupling between one set of anode sections and the cathode on the one hand and that existing between the other set of anode sections and the cathode on the other. Since this type of cathode coupled output is particularly useful in voltage tuned devices and electron injection is particularly applicable to controlling the number of electrons in the inner electrode space in voltage tunable systems, the present invention involves a structure in which electron in ection is provided in combination with the desired un- 'baltanced coupling between the anode and cathode circurs.

In the particular embodiment illustrated the device provides for a concentric line to waveguide transition. While this is a desirable electrical and mechanical arrangement for many applications it is to be appreciated that in its broader aspects the present invention may be applied to a concentric line output and it will be appreciated also that the cathode circuit may be effectively extended to the envelope either directly or by a.capacitive coupling and the outer conductor of the concentric line may be coupled to the anode terminal 15.

While We have shown and described a particular embodiment of our invention it will be apparent to those skilled in the art that changes and modifications may be made without departing from our invention in its broader aspects, and we aim, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.'

What we claim as new and desire to secure byLetters Patent of the United States is:

l. A magnetron system comprising a generally annular cavity resonator provided with opposed end walls, a plurality of anode sections providing the inner wall of said resonator with alternate anode sections connected to a different one of said opposite end walls of said cavity resonator, a cathode structure providing a source of electrons including a generally cylindrical portion received within the opening in said cavity resonator and defining therewith an interaction space, means providing a substantially larger coupling capacity between the anode sections connected to one of the opposed end walls of said cavity resonator and said cathode structure than between the anode sections connected to the other end of the opposed end walls of said cavity resonator and said cathode structure and an output circuit coupled between said cathode and the anodesections connected to the other of said opposed end walls of said cavity resonator.

2. A magnetron system comprising an anode structure including two sets of anode sections, alternately arranged in a generally cylindrical array, a cathode structure providing a source of electrons including a generally cylindrical portion received within the opening defined by said array of anode sections and defining therewith an interaction space, means providing a substantially larger coupling capacity between one set of anode sections and said cathode structure than the capacity coupling between the other set of anode sections and said cathode struc ture and an output circuit coupled between said cathode structure and said other set of anode segments.

3. A magnetron system comprising an anode structure including two sets of anode sections alternately arranged in a generally cylindrical array, a cathode structure providing a source of electrons including a generally cylindrical non-emitting portion received within the opening defined by said array of anode sections and defining therewith an interaction space and an electron emitting portion axially displaced from said non-emitting portion, a control member surrounding said emitting portion and providing a substantially larger coupling capacity between one set of anode sections and said cathode structure than the capacity coupling between the other set of anode sections and said cathode structure and an output circuit coupled between said cathode structure and said other set of anode segments.

4. A magnetron system comprising an anode structure including two sets of anode sections alternately arranged in a generally cylindrical array, a cathode structure providing a source of electrons including a generally cylindxical portion received within the opening defined by said array of anode sections and defining therewith an interaction space, means providing a substantially larger coupling capacity between one set of anode sections and one end of said cathode structure than the capacity coupling between the other set of anode sections and said cathode structure and an output circuit coupled between the other end of said cathode structure and said other set of anode segments. I

5. A magnetron system comprising an anode structure including two sets of anode sections alternately arranged in a generally cylindrical array, a cathode structure providing a source of electrons including a generally cylindrical portion received within the opening defined by said array of anode sections and defining therewith an interaction space, means providing a substantially larger coupling capacity between one set of anode sections and one end of said cathode structure than the capacity coupling between the other set of anode sectionsand said cathode structure and an output circuit having spaced walls with one wall coupled to the other end of said cathode structure and the other of said spaced walls coupled to said other set of anode segments.

References Cited in the file of this patent UNITED STATES PATENTS 2,810,096 Peters Oct. 15, 1957 

